Troubleshooting Adhesion Problems with Two-Part Polyurethane Over Danish Oil

      Feedback for a finisher who is seeing 2k poly pull away when applied over an oil-based coating. September 25, 2014

Question (WOODWEB Member) :
We are currently constructing commercial bar tops for a popular local watering hole who is adding a large addition. The bar tops are constructed of 8/4 hard maple with cherry accents. We chose to use ML Campbell Eurobild 2K polyurethane. We started by applying two coats of Natural Watco Danish Oil to bring out the grain of the wood which was allowed to dry for about three weeks. We then lightly sanded the tops with 220 grit before proceeding with the application of the Eurobild. I applied two coats of Eurobild high solids sealer following the manufactures guidelines to the T.

The next day after sufficient drying time the sealer was sanded with 220 and three coats of Eurobild Clear 2K polyurethane EU30372 were applied as per the manufactures guidelines. I then waited overnight (about 18 hours) and began to lightly sand with 220 grit in preparation of a final top coat.

While sanding, the topcoat began separating from the sealer. I was able to just scrape off the finish with my thumbnail. There was no adhesion between the sealer and the top coat. Every step was followed precisely as far as material and catalyst mixing ratios, environmental requirements and time between coats and time before sanding. I have tried this whole process twice, once with replacement material from the manufacturer (however it was the same batch) with the same result both times. I am at a loss and need to get this project out the door. I would appreciate any advice or insight from people who have experience with this product of type of products.

Forum Responses
(Finishing Forum)
From contributor C:
I would use a barrier coat after the Watco, better yet would have been to use a dye stain to highlight the grain. MLC has a Euro exotic wood sealer EU32079 to use as a sealer over oily woods. I've had polyester peel off when I did not use a barrier coat.

From Contributor B:
Don't use Danish Oil under a urethane. If you have to use an oil stain, use Woodsong II or something similar, and use the Isolante - Barrier Coat.

From Contributor J:
As mentioned above using 2k 's with any oily substance or wood species an isolante barrier coat is required . My hunch is your seeing the sealer and top coat releasing from the oiled layer. Also when a Danish Oil is sanded using a fine grit it gets glassy rather quickly using a stain base lightly tinted would be a better option to highlight the grain when using 2k's.

From the original questioner:
There is no adhesion issue with the sealer to the substrate. The sealer can barely be scraped of and if I did want to remove it, it would be very difficult. I will try testing the system on a piece of bare maple to see if the Danish Oil may be the culprit and keep you posted on the results.

From contributor J:
I'm curious why you used two coats of Watco. What did you gain from the second? It gets oilier after the first coat.

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